The present invention generally relates to a facsimile transceiver and, more particularly, to an improved printing system for a facsimile reception apparatus for receiving and printing transmitted data in compressed form.
Facsimile transmission systems are extremely useful for transmitting original documents in numerous commercial and bureaucratic applications. The original document is scanned to produce electrical signals which are transmitted over a telephone line or the like to a remote receiver. The receiver prints a facsimile or reproduction of the original document in response to the received signals. Further, it is presently common to compress the signals for transmission using run length encoding or the like in order to increase the transmission speed.
A modern high-speed facsimile transceiver equipped with a compression device for the above purpose is designed to read data from an original document or write them in at a specific speed which corresponds to a density of the data. For this reason, a paper sheet as a recording medium is fed intermittently at a variable speed in accordance with a compressed signal particularly in a printing system at the receiver, more particularly in an electrostatic recording device of the printing system. Therefore, if an ordinary heat type fixing device were used to process a toner image on a sheet, the amount of radiated heat might be too small to fuse toner particles on the sheet or so large as to burn the sheet.
Efforts heretofore made to settle this problem may be represented by the system disclosed in Japanese Patent Publication No. 53-19032. In this system, a fixing unit employing a xenon lamp is disposed in a fixing station while a sheet feed roller is positioned past of the fixing station and driven by a stepping motor. Pulses supplied to the stepping motor are counted to energize the lamp at a proper timing for fixation. However, such a system cannot avoid drawbacks in various aspects. The stepping motor needs be of a significantly large torque since it has to feed a sheet from a latent image forming station all the way to the developing and fixing stations without any assistance. Also, such a manner of sheet feed lacks precision in the latent image forming station. Because a cutter must be located in a position past of the sheet feed roller, a disproportionate blank area is produced at the leading end of the first copy sheet. Additionally, an intricate circuit arrangement is required for energizing the lamp at an adequate timing.
In a dry process developing device, a magnet roller is usually driven by an a.c. motor at a constant speed. Thus, concerning the prior art system described above, the sheet travelling speed and the peripheral speed of the magnet roller is constantly varied relative to each other inviting an irregular density distribution in reproduced images.